Unity Manual

Shader data types and precision

The standard ShaderA built-in shader for rendering real-world objects such as stone, wood, glass, plastic and metal. Supports a wide range of shader types and combinations. More infoSee in Glossary language in Unity is HLSL, and general HLSL data types are supported. However, Unity has some additions to the HLSL types, particularly for better support on mobile platforms.

Basic data types

The majority of calculations in shadersA small script that contains the mathematical calculations and algorithms for calculating the Color of each pixel rendered, based on the lighting input and the Material configuration. More infoSee in Glossary are carried out on floating-point numbers (which would be float in regular programming languages like C#). Several variants of floating point types are present: float, half and fixed (as well as vector/matrix variants of them, such as half3 and float4x4). These types differ in precision (and, consequently, performance or power usage):

Integer data types

Integers (int data type) are often used as loop counters or array indices. For this purpose, they generally work fine across various platforms.

Depending on the platform, integer types might not be supported by the GPU. For example, Direct3D 9 and OpenGL ES 2.0 GPUs only operate on floating point data, and simple-looking integer expressions (involving bit or logical operations) might be emulated using fairly complicated floating point math instructions.

Direct3D 11, OpenGL ES 3, Metal and other modern platforms have proper support for integer data types, so using bit shifts and bit masking works as expected.

Composite vector/matrix types

HLSL has built-in vector and matrix types that are created from the basic types. For example, float3 is a 3D vector with .x, .y, .z components, and half4 is a medium precision 4D vector with .x, .y, .z, .w components. Alternatively, vectors can be indexed using .r, .g, .b, .a components, which is useful when working on colors.

Matrix types are built in a similar way; for example float4x4 is a 4x4 transformation matrix. Note that some platforms only support square matrices, most notably OpenGL ES 2.0.

Texture/Sampler types

Typically you declare textures in your HLSL code as follows:

sampler2D _MainTex;
samplerCUBE _Cubemap;

For mobile platforms, these translate into “low precision samplers”, i.e. the textures are expected to have low precision data in them. If you know your texture contains HDRhigh dymanic range See in Glossary colors, you might want to use half precision sampler:

sampler2D_half _MainTex;
samplerCUBE_half _Cubemap;

Or if your texture contains full float precision data (e.g. depth texture), use a full precision sampler:

sampler2D_float _MainTex;
samplerCUBE_float _Cubemap;

Precision, Hardware Support and Performance

One complication of float/half/fixed data type usage is that PC GPUs are always high precision. That is, for all the PC (Windows/Mac/Linux) GPUs, it does not matter whether you write float, half or fixed data types in your shaders. They always compute everything in full 32-bit floating point precision.

The half and fixed types only become relevant when targeting mobile GPUs, where these types primarily exist for power (and sometimes performance) constraints. Keep in mind that you need to test your shaders on mobile to see whether or not you are running into precision/numerical issues.

Even on mobile GPUs, the different precision support varies between GPU families. Here’s an overview of how each mobile GPU family treats each floating point type (indicated by the number of bits used for it):

GPU Family

float

half

fixed

PowerVR Series 6/7

32

16

PowerVR SGX 5xx

32

16

11

Qualcomm Adreno 4xx/3xx

32

16

Qualcomm Adreno 2xx

32 vertex 24 fragment

ARM Mali T6xx/7xx

32

16

ARM Mali 400/450

32 vertex 16 fragment

NVIDIA X1

32

16

NVIDIA K1

32

NVIDIA Tegra 3/4

32

16

Most modern mobile GPUs actually only support either 32-bit numbers (used for float type) or 16-bit numbers (used for both half and fixed types). Some older GPUs have different precisions for vertex shaderA program that runs on each vertex of a 3D model when the model is being rendered. More infoSee in Glossary and fragment shaderThe “per-pixel” part of shader code, performed every pixel that an object occupies on-screen. The fragment shader part is usually used to calculate and output the color of each pixel. More infoSee in Glossary computations.

Using lower precision can often be faster, either due to improved GPU register allocation, or due to special “fast path” execution units for certain lower-precision math operations. Even when there’s no raw performance advantage, using lower precision often uses less power on the GPU, leading to better battery life.

A general rule of thumb is to start with half precision for everything except positions and texture coordinates. Only increase precision if half precision is not enough for some parts of the computation.

Support for infinities, NaNs and other special floating point values

Support for special floating point values can be different depending on which (mostly mobile) GPU family you’re running.

All PC GPUs that support Direct3D 10 support very well-specified IEEE 754 floating point standard. This means that float numbers behave exactly like they do in regular programming languages on the CPU.

Mobile GPUs can have slightly different levels of support. On some, dividing zero by zero might result in a NaN (“not a number”); on others it might result in infinity, zero or any other unspecified value. Make sure to test your shaders on the target device to check they are supported.

External GPU Documentation

GPU vendors have in-depth guides about the performance and capabilities of their GPUs. See these for details: